A time division multiple access (TDMA) based system may be distributed and centralized in nature. Centralized TDMA system consists of a controller or central hub, and multiple devices wirelessly connected to the controller. The controller is an entity responsible for creation and management of a centralized TDMA based network. Typically, the controller divides available time into multiple slots and defines a fixed period (superframe) containing fixed number of slots. Each device is allocated one or more slots for its data transmission.
Device oscillators often have a slight random deviation from their normal frequency, called clock skew. When clock drifts occur, a communication device may transmit earlier or later than the specified slot allocated to it. This means that, there is a shift either to the right or to the left in the time domain depending on the difference in the rate of the clock drifts between any two devices. Due to clock skew, the communication devices may get de-synchronized during the course of time with the controller. In order to keep the devices synchronized with the controller, the controller periodically transmits a special frame called ‘beacon frame’. The devices listen for the beacon to remain synchronized with the controller and transmit data in their allocated time slot. This allows the devices to duty cycle when they don't have any data to transmit or not expecting any data from the controller, thereby conserving power.